The present invention is directed to aluminum alloys that are clad or any other aluminum product covered with a protective aluminum or aluminum alloy ("Alclad") wherein a liner covering is inset into a grooved ingot and subsequently roll bonded to the core alloy to make an integral structure.
A problem in the aerospace alloy art is the corrosion resistance or lack thereof, of certain aerospace alloys that are used to build fuselage structures of today's commercial airlines. Past practice has solved this corrosion problem by cladding or covering the aerospace alloy with an alloy that does not contain the strength or toughness properties of an aerospace alloy but instead provides a significant improvement in corrosion resistance and weathering effects.
As the practice of Alcladding is performed today, an ingot of alloyed aluminum is covered with a higher purity aluminum, for instance a 1xxx series aluminum alloy as designated by the Aluminum Association registration, or simply pure aluminum. As those who come to appreciate the invention hereof will realize this invention can also be applied to the brazing sheet art which generally sandwiches 3xxx and 4xxx alloys. To cover an aerospace alloy such as 2xxx or 7xxx or marine alloy such as the 3xxx, 5xxx, and/or the 6xxx series alloys, the higher purity aluminum must be bonded in some way to the core alloy. This is typically done today by hot rolling. Hot rolling or working the aluminum alloy and Alclad together effectively forces the metal and alloy to combine as a single sandwich structure. As the force and heat of the hot rolls compress the alloy and metal together excess metal cladding peels at the edges of the sandwich structure. This peeling is believed to be inherent to the hot rolling Alclad process due to a difference in yield strength between the harder and tougher core alloy ingot and the Alclad liner material. Nonetheless, the peeling must be removed prior to finishing the hot rolling of the sandwich structure. Failure to remove the peeling will result in product unacceptable to the customer. Having to remove the peeling has proven both an economic and worker safety liability. The need to remove the peeling requires an employee to enter a hot mill area, climb onto the hot mill equipment and lift and remove the peelings. That this can be a significant event is reflected by the conditions at the hot mill. The temperatures of the peelings and Alclad sandwich in this environment can range from 450 degrees F. to 850 degrees F. and the peelings weight may range from 1 pound to as much as 200 pounds.
Working an alloy can mean hot rolling, cold rolling, annealing, solution hot treating, aging, forging, and extruding. Generally, working an alloy means adding energy to the alloy from some source through a process.
Accordingly, the practice described hereof pleads for improvement. Improvement of this practice is the subject of the present invention. Hereof, simplicity of thought has brought this Alcladding process into the realm of reasonability. Replacing the forced Alclad as the metal of least resistance and therefore the metal that peels, the Alclad material of the present invention is protected in the hot rolling process by being inset into a grooved out core alloy and then subsequently hot rolled and/or further worked.